"The information that we have is that there was a shot to the throat," he said.

"It doesn't mean he can't communicate, but right now I think he's in a condition where we can't get any information from him at all," he added.

"We are now reliably informed he has a gunshot wound, a very serious one, to his throat as well as other gunshot wounds to his leg, but it's the injury to his throat that has meant the special investigation, interrogation team that has been at the hospital waiting to speak to him means that they have not been able to have that communication.

He's heavily sedated, not in a coma but heavily sedated.

He's breathing through a tube and they describe his condition as extremely serious.

North America correspondent Lisa Millar

The Chechen-born brothers are suspected of staging the twin bombing attacks on the Boston Marathon which killed three people and injured almost 180.

US attorney Carmen Ortiz, the federal prosecutor for the Boston area, is working on filing criminal charges, Boston Police Commissioner Ed Davis said.

Boston bombings timeline

The most serious charge available to federal prosecutors is use of a weapon of mass destruction to kill people. It carries a possible death sentence.

The two brothers may have been readying for a second attack at the time of the shootout, Commissioner Davis said.

"We have reason to believe, based upon the evidence that was found at that scene [of the gunfight], the explosions, the explosive ordnance that was unexploded, and the firepower that they had, that they were going to attack other individuals," Commissioner Davis told CBS.

Tamerlan posted militant Islamist videos on social media sites and made a six-month trip to Russia's volatile Caucasus region last year.

Much of what he did on the trip is still a mystery to US investigators.

Neighbours contacted by Reuters say he spent at least a few weeks in Dagestan, a predominantly Muslim region in the North Caucasus mountains where Islamist militants have long been a thorn in the side of governments in Moscow.

"I personally believe this man received training when he was over there and he radicalised," Mr McCaul, a Texas Republican, told CNN.

"If he was on the radar and they let him go, he's on the Russians' radar, why wasn't a flag put on him, some sort of customs flag?"

"The ball was dropped. I don't know if our laws are insufficient or the FBI failed," he said.

Asked overnight about lawmakers' concerns, the FBI said it had no further comment beyond an earlier statement when it said it "did not find any terrorism activity, domestic or foreign" after speaking to Tamerlan and checking his travel records and internet activity.

House Intelligence Committee chairman Mike Rogers, a former FBI agent, defended the agency, saying it had performed a "very thorough" review in 2011 but failed to receive further cooperation from Russia.

The FBI interview and an allegation of domestic abuse against a girlfriend raised concerns when Tamerlan applied for US citizenship last year.

Since the airing of the gut-wrenching documentary Leaving Neverland, many of us have wrestled with an uncomfortable, yet essential question: given everything we know, can we continue listening to Michael Jackson's music?